The reaction mechanisms of a number of flavoproteins will investigated. These include representative examples from the various classes of flavoproteins, e.g., flavodoxin as an electron transferase; D-lactate dehydrogenase and "Electron Transfer Flavoprotein" as examples of transhydrogenases; glucose oxidase, L-lactate oxidase, and D-amimo acid oxidase as typical oxidase flavoproteins; melitotate and p-hydroxybanzoate hydroxylases as examples of flavoprotein monooxygenases; xanthine oxidase as an example of a complex flavoprotein with multiple redox groups. Considerable use will be made of steady-state kinetics coupled with rapid reaction kinetic studies, in order to detect and characterize reaction intermediates, and to test their catalytic involvement. We also plan to make extensive use of flavin replacement studies, where the native flavin is removed and replaced by an artificial one. In this way the redox potential may be varied and the importance of that parameter established. More importantly, it is hoped that the changed chemical properties of the new flavin may give useful mechanistic information by resulting in changed behavior of intermediates.